This invention relates to novel copolymers of maleic anhydride with acrylic or methacrylic acid, a process for their preparation and their use in hydrolyzed form as antiscalants.
Aqueous systems containing dissolved mineral salts are commonly employed in operations such as heating, cooling and evaporative distillation which involve heat transfer. The salts often become insoluble during the operation and are deposited as scale on the heat transfer surfaces, resulting in reduced heat transfer and eventual failure of the equipment. In general, the mineral scale salts are derived from alkaline earth and other metal cations such as calcium, magnesium, iron and lead, and from anions such as bicarbonate, carbonate, hydroxide, sulfate and phosphate. Many factors influence scale formation and include, for example, the pH of the water, the nature of the dissolved salts and the temperature of the operation.
Numerous additives have been proposed as inhibitors of mineral scaling. Included are polymaleic acid and copolymers of maleic acid with such as acrylic and methacrylic acids. A variety of approaches to the preparation of these acrylate/maleate copolymers has been reported, such preparations being disclosed, for example, in U.S. Pat. Nos. 3,635,915 and 3,755,264, British Patent Specification No. 1,414,918 and Netherlands Application No. 7506874. The disclosed preparations, however, result in a product which is not a true copolymer but rather a mixture of essentially homopolymers. It is therefore an objective of the present invention to provide a process for the preparation of substantially homogeneous acrylate/maleate copolymers which have improved antiscalant activity and reduced residual monomer content.